For example, U.S. Pat. No. 5,383,546 to Argen J. Mulder discloses a device for detecting a foreign body or string in a coin channel when the string connected to a coin is drawn to string or illegally take out the coin from coin channel. The device comprises an infrared emitter, and an infrared sensor for detecting infrared ray emitted from the emitter and reflected on the string.
U.S. Pat. No. 5,806,649 to Michael Walsh, et al., demonstrates a paper currency validator which comprises an LED and light receiver mounted at opposite sides of a wiring board for a bill checker across a bill passageway in the validator to detect a foreign object in the passageway in terms of amount in light emitted from the LED and sensed by the light receiver.
U.S. Pat. No. 5,988,345 to Alfred F. Gergeron, et al., represents a bill validator which comprises an LED and a photo-transistor located opposite to and in spaced relation to each other beneath a bill passageway in the validator, a first prism for laterally reflecting light from the diode into the passageway, a second prism for again reflecting light from the first prism toward the photo-transistor across the passageway to detect a foreign matter in the passageway in view of output from the photo-transistor.
In this way, typical prior art optical device for detecting extraneous object, employs a plastic-encapsulated LED device for irradiating light interior of bill passageway. A plastic encapsulant of typical LED device is conventionally formed into a cannonball or shell shape with a hemispherical top end to provide an optical hemispherical lens for converging to some extent light emitted from the diode device toward a light detector. However, such an LED of shell shape is disadvantageous in that it radially illuminate or radiates light diverging toward an irradiance circle section which would incur loss of light dispersed in an irrelevant irradiative direction to light detector. Upon detecting an object in bill passageway by means of light emitted from LED device, such dispersed light radiation may unfavorably deteriorate accurate detection of the object because scattering of light reduces amount of light reaching the detector which therefore cannot appreciate the difference in amount of received light between a bright condition without object and a shadow condition with object in bill passageway.
An object of the present invention is to provide an LED device having the wider light directivity angular range in a necessary irradiative direction. Another object of the present invention is to provide an LED device having a cylindrical lens which can converge light from an LED chip to a linear beam section widened in a first irradiative direction and narrowed in a second irradiative direction different from the first irradiative direction. A still another object of the present invention is to provide an optical detector incorporating the LED device for a bill validator.